1. Field of the Invention
This invention relates to a controller for controlling a generator mounted on a vehicle such as an automobile.
2. Description of the Prior Art
FIG. 5 is a circuit diagram of a controller for a car generator of the prior art disclosed in Laid-open Japanese Patent Application No. Sho 62-104500. In FIG. 5, reference numeral 1 denotes an AC generator having an armature coil 101 and a field coil 102. Reference numeral 2 denotes a full-wave rectifier having rectifying diodes 203 to 208 for rectifying the output of the AC generator 1, 201 a positive-side output terminal of the full-wave rectifier 2 and 202 is a negative-side output terminal of the full-wave rectifier 2. Numeral 3 designates a voltage regulator for regulating the output voltage of the AC generator 1 to a predetermined value and having a power transistor 301 for controlling a field current running through the field coil 102 of the AC generator 1 intermittently. A current detection resistor 302 is connected to the emitter of the power transistor 301 and to the ground. A field current limiter 4 is provided for limiting the maximum value of a field current running through the field coil 102 to a predetermined value. This field current limiter 4 has a comparator 403 for comparing a field current detected by the current detection resistor 302 of the voltage regulator 3 with a set value obtained by dividing a voltage from a constant voltage source A by voltage dividing resistors 401 and 402 to control the power transistor 301 of the voltage regulator 3. A storage battery 5 is charged by the rectified output of the AC generator 1.
FIG. 4 is a diagram showing the output characteristics of the controller of the prior art with respect to the temperature of the generator and the output characteristics of the controllers of Embodiments 1, 2 and 3 of the present invention to be described hereinafter with respect to the temperature of the generator. In the relationship between the temperature of the generator and the field current of FIG. 4, 54 indicates the output characteristics of the generator itself and 55 the output characteristics of the controller of the prior art. In the relationship between the temperature of the generator and the output current of the generator, 51 indicates the output characteristics of the generator itself and 52 the output characteristics of the controller of the prior art. In the case of the controller of the prior art, as shown in FIG. 4, the field current is controlled not to exceed a predetermined value at a temperature below a predetermined temperature (output characteristics 52 and 55).
In the case of the controller for a car generator of the prior art as described above, though the field current of the generator when it is cold can be limited to a level when it is hot, it is impossible to meet a demand for reducing the drive torque of the generator when it is cold. Therefore, especially at low temperatures, the drive torque load affects the internal combustion engine which is a drive source for the generator with the result that the startability and revolution stability right after start-up of the internal combustion engine deteriorate. Further, when the limitation amount at low temperatures is made large, the output of the generator at an actual temperature range is reduced.